In a news conference at his alma mater, the University of South Dakota, Johnson joked, "I will be 68 years old at the end of this term and it is time for me to say goodbye. As much as [my wife] Barbara would like me to run again, I have to say no,” and went on to say, "I'm honored and humbled that the people of South Dakota, Democrats, Republicans and independents, have allowed me to represent you in the state legislature, the United States House of Representatives and the U.S. Senate."[1]

Johnson was first elected to the U.S. Senate in 1996 and won re-election in 2002.[2] In 2006, Johnson suffered a brain hemorrhage that almost killed him, but he recovered and went on to run for and win re-election in 2008.[2] When asked if his health was behind his decision not to run again, Johnson answered "I feel great, but I must be honest. I appreciate that my right arm and right leg are not what they used to be and my speech is not entirely there. But I think mostly that it's time to go."[2]

If he had made a bid for another term in the Senate, Johnson was expected to face a tough win for re-election, and was considered vulnerable.[3]